Debt Service Coverage Ratio for Floating Rate Commercial Mortgage Loans by Property Type (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	$ 5,868	$ 5,912
% of total	100.00%	100.00%
Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	184	260
% of total	100.00%	100.00%
Weighted-average loan-to-value	63.00%	78.00%
Retail
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	2,000	1,895
% of total	34.00%	32.00%
Retail | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	103	104
Office
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	1,585	1,580
% of total	27.00%	27.00%
Office | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	76	84
Industrial
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	1,565	1,603
% of total	27.00%	27.00%
Industrial | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	5	6
Apartments
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	490	552
% of total	8.00%	9.00%
Apartments | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	0	0
Mixed use/other
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	228	282
% of total	4.00%	5.00%
Mixed use/other | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	0	66
Less than 1.00 | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	0	0
% of total	0.00%	0.00%
Weighted-average loan-to-value	0.00%	0.00%
Less than 1.00 | Retail | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	0	0
Less than 1.00 | Office | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	0	0
Less than 1.00 | Industrial | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	0	0
Less than 1.00 | Apartments | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	0	0
Less than 1.00 | Mixed use/other | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	0	0
1.00 - 1.25 | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	0	0
% of total	0.00%	0.00%
Weighted-average loan-to-value	0.00%	0.00%
1.00 - 1.25 | Retail | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	0	0
1.00 - 1.25 | Office | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	0	0
1.00 - 1.25 | Industrial | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	0	0
1.00 - 1.25 | Apartments | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	0	0
1.00 - 1.25 | Mixed use/other | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	0	0
1.26 - 1.50 | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	8	9
% of total	4.00%	3.00%
Weighted-average loan-to-value	78.00%	55.00%
1.26 - 1.50 | Retail | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	0	1
1.26 - 1.50 | Office | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	8	8
1.26 - 1.50 | Industrial | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	0	0
1.26 - 1.50 | Apartments | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	0	0
1.26 - 1.50 | Mixed use/other | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	0	0
1.51 - 2.00 | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	1	0
% of total	1.00%	0.00%
Weighted-average loan-to-value	6.00%	0.00%
1.51 - 2.00 | Retail | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	1	0
1.51 - 2.00 | Office | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	0	0
1.51 - 2.00 | Industrial | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	0	0
1.51 - 2.00 | Apartments | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	0	0
1.51 - 2.00 | Mixed use/other | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	0	0
Greater than 2.00 | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	175	251
% of total	95.00%	97.00%
Weighted-average loan-to-value	63.00%	79.00%
Greater than 2.00 | Retail | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	102	103
Greater than 2.00 | Office | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	68	76
Greater than 2.00 | Industrial | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	5	6
Greater than 2.00 | Apartments | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	0	0
Greater than 2.00 | Mixed use/other | Floating Rate Commercial Mortgage Loans
Commercial Mortgage Loans by Credit Quality Indicator [Line Items]
Commercial mortgage loans, recorded investment	$ 0	$ 66